US5289539A - Echo canceller using impulse response estimating method - Google Patents

Echo canceller using impulse response estimating method Download PDF

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Publication number
US5289539A
US5289539A US07/757,951 US75795191A US5289539A US 5289539 A US5289539 A US 5289539A US 75795191 A US75795191 A US 75795191A US 5289539 A US5289539 A US 5289539A
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echo
signal
output
circuit
impulse response
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Yuisuke Maruyama
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NEC Corp
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NEC Corp
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04M—TELEPHONIC COMMUNICATION
    • H04M9/00—Arrangements for interconnection not involving centralised switching
    • H04M9/08—Two-way loud-speaking telephone systems with means for conditioning the signal, e.g. for suppressing echoes for one or both directions of traffic
    • H04M9/082—Two-way loud-speaking telephone systems with means for conditioning the signal, e.g. for suppressing echoes for one or both directions of traffic using echo cancellers
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B3/00—Line transmission systems
    • H04B3/02—Details
    • H04B3/20—Reducing echo effects or singing; Opening or closing transmitting path; Conditioning for transmission in one direction or the other
    • H04B3/23—Reducing echo effects or singing; Opening or closing transmitting path; Conditioning for transmission in one direction or the other using a replica of transmitted signal in the time domain, e.g. echo cancellers

Definitions

  • the present invention relates to an echo canceller using an FIR filter and, more particularly, to an echo canceller which increases the converging speed of an FIR filter.
  • a typical application of an echo canceller is to a hybrid transformer which implements the 2-wire/4-wire conversion of a telephone line or satellite communication line and generates an echo due to impedance mismatching between the 2-wire path and the 4-wire path.
  • Another typical application is to a TV conference system or a voice conference system in which a loudspeaker and a microphone are acoustically coupled to generate an echo.
  • an FIR filter estimates the impulse response of an echo path from a received input signal and then generates an estimated echo signal. The estimation of an impulse response requires multiplication and addition steps to be repeated a number of times within a short period of time. The number of such arithmetic operations increases with the duration of the impulse response.
  • the multiplication and addition steps have to be repeated several hundred times within about 100 milliseconds in the case of the estimation of an echo ascribable to the hybrid transformer of a telephone line or even several thousand times when it comes to the estimation of an echo ascribable to the turn-around of a speaker output to a microphone.
  • various kinds of methods such as a normalized LMS (Least Mean Square) method and an RLS (Recursive Least Square) method.
  • the normalized LMS method may be denoted as follows:
  • y(j), y(j), e(j) and x(j) are respectively the estimated echo signal, transmission input signal, transmission output signal (difference output signal), difference between y(k) and y(k)) and received input signal at a particular time j.
  • a received input vector X(j) and an estimated impulse response vector H(j) at a time j are defined as:
  • hi(j) is the estimated impulse response at a tap position i and at a time j.
  • ⁇ is a constant which is greater than zero and smaller than 2; the converging speed is highest when ⁇ is 1.
  • An echo canceller of the type which estimates an echo by the normalized LMS method is disclosed by, for example, YING G. TAO in "A Cascadable VLSI Echo Canceller", IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS, VOL. SAC-2, March 1984, pp. 297-303. Since the normalized LMS method is based on a statistical procedure, convergence occurs most rapidly with an input signal having no correlation, i.e., white noise. The maximum converging speed depends on the estimation order of the filter, and the convergence is completed after a number of repetitions which is about twenty times as great as the estimation order (about 30 dB in terms of the amount of echo cancellation).
  • the estimation order (number of taps) of the filter should be at least about 2,000 even when the sampling frequency is as high as 8 kilohertz, i.e., even then, more than five seconds is necessary for convergence. It follows that when the initial convergence of the path is changed, the echo is noticeably increased, which degrades the conversation quality in the communication system.
  • an echo canceller using the RLS method has also been proposed, which solves simultaneous equations to thereby produce an impulse response sequence H(j) uniformly.
  • the RLS method is not practicable since it requires a prohibitive number of arithmetic operations, although it promotes rapid convergence and copes with changes of the initial convergence and path change, by comparison with the normalized LMS method.
  • an object of the present invention to provide an FIR type echo canceller capable of promoting rapid convergence while reducing the ratio of increase in the required number of calculations.
  • an echo canceller for removing an echo signal, ascribable to the turn-around of a received signal to become a transmission signal to thereby output a signal with such echo cancelled, comprises impulse response estimating means for estimating the impulse response of the echo path at a time t in response to the received signal, the echo cancelled signal, and an estimated impulse response signal, thereby outputting the estimated impulse response as the estimated impulse response signal; echo signal estimating means for determining a predicted signal representative of a predicted echo signal from the estimated impulse response signal and the received signal, and outputting the predicted signal as an estimated echo signal; and subtractor means for subtracting the estimated echo signal from the transmission signal to produce the echo cancelled signal.
  • the impulse response estimating means estimates the impulse response of the echo path as a function of the received signal and echo cancelled signal at the time t, and the received signal and echo cancelled signal at a time (t-M) (M being a natural number).
  • FIG. 1 is a block diagram schematically showing an echo canceller embodying the present invention
  • FIG. 2 is a circuit diagram showing a specific construction of a correction coefficient calculating circuit included in the embodiment of FIG. 1 and implemented with the normalized LMS method;
  • FIG. 3 is a circuit diagram similar to FIG. 2, showing another specific construction of the correction coefficient calculating circuit implemented with the LMS method.
  • FIG. 4 is a block diagram schematically showing an alternative embodiment of the present invention.
  • the normalized LMS method estimates the impulse response of an echo path on the assumption that the received input vector appears randomly in the statistical aspect.
  • the estimation of the impulse response is not practicable unless sampling is repeated a number of times ten to twenty times as great as the number of taps.
  • an echo canceller embodying the present invention is shown to which the normalized LMS method is applied.
  • the echo canceller has first second and third N-sample memories 1-3, first and second M-sample delay circuits 20 and 21, first and second correction coefficient calculating circuits 30 and 31, first and second convolution circuits 10 and 11, first and second subtractors 40 and 41, first and second adders 50 and 51, and first and second multipliers 60 and 61.
  • a received input signal x(j) is applied to the first N-sample memory 1 and first M-sample delay circuit 20.
  • the N-sample memory 1 stores the N latest received input signals at any given time, i.e., it removes the oldest x(j-N) on receiving x(j).
  • the M-sample delay circuit 20 delays the received input signal x(j) by M samples to output a delayed received input signal x(j-M). Further, the received input signal x(j) is applied to the first correction coefficient calculating circuit 30 and used to produce a first correction coefficient ⁇ h(j) which will be described later.
  • the delayed received input signal x(j-M) is fed to the third N-sample memory 3 and second correction coefficient calculating circuit 31.
  • the third N-sample memory 3 may have the same construction as the first N-sample memory 1 and stores the N latest delayed received input signals at a given time. Having the same construction as the first correction coefficient calculating circuit 30, the second correction coefficient calculating circuit 31 produces a second correction coefficient ⁇ h(j-M) in response to a first echo-cancelled signal e(j-M) fed from the second subtractor 41 and the first delayed received input signal x(j-M).
  • the convolution circuit 10 determines an estimated echo y associated with a transmission input signal y(j) according to the equation (4).
  • the second convolution circuit 11 receives the M-sample delayed received input signal vector X(j-M) and the impulse response vector H(j) from the third and second N-sample memory 3 and 2, respectively, and determines an estimated echo y(j-M) associated with an M-sample delayed transmission input signal y(j-M) according to the equation (5).
  • the first subtractor 40 subtracts the estimated echo y(j) outputted by the first convolution circuit 10 from the transmission input signal y(j), outputting the resulted difference as a transmission output signal e(j).
  • the transmission output signal e(j) is applied to the first correction coefficient calculating circuit 30 also.
  • the second M-sample delay circuit 21 delays the transmission input signal y(j) by M samples to produce a delayed transmission input signal y(j-M).
  • the second subtractor 41 subtracts the estimated echo y(j-M) outputted by the second convolution circuit 11 from the delayed transmission input signal Y(j-M), feeding the resulted difference signal e(j-M) to the second correction coefficient calculating circuit 31.
  • the first multiplier 60 multiplies the first correction coefficient ⁇ h(j) and the corresponding element of the received input signal vector X(j) to produce ⁇ h(j) X(j).
  • the first adder 50 adds H(j) to ⁇ h(j) X(j) to output H(j)+ ⁇ h(j) X(j).
  • the second multiplier 61 produces ⁇ h(j-M)X(J-M).
  • the second adder 51 outputs H(j+1) (equation 8) and feeds it to the second N-sample memory 2.
  • control over the write-in and read-out of the first to third N-sample memories 1-3 and the output of the first and second correction coefficient calculating circuits can be readily implemented by a microprocessor, counter, etc., although those elements are not shown in the figure.
  • FIG. 2 shows a specific construction of the first correction coefficient calculating circuit 30 in FIG. 1.
  • the correction coefficient calculating circuit 30 is made up of a power calculating circuit 71 having an N-sample memory, and a dividing circuit 70.
  • FIG. 2 represents a case wherein the speed coefficient ⁇ is 1.
  • the received input signal x(j) is written to the N-sample memory of the power calculating circuit 71 and, at the same time, is used to calculate the power of N samples ⁇ x 2 (j), i.e., X(j) ⁇ X(j) together with the past (N-1) samples.
  • the dividing circuit 70 divides the transmission output signal e(j) from the first subtractor 40 by the power ⁇ x 2 (j) to produce e(j)/(X(j) ⁇ X(j) as ⁇ h(j).
  • ⁇ is not 1
  • a multiplier for multiplying the output of the dividing circuit 70 by ⁇ may be used.
  • the second correction coefficient calculating circuit 31 may have the same construction as the circuit 30.
  • FIG. 3 shows another specific construction of the correction coefficient calculating circuit 30 which is applicable to the LMS scheme wherein no normalization by the received input signal x(j) is effected.
  • the circuit 30 multiplies the transmission output signal e(j) by a predetermined scaling factor ⁇ by means of a multiplier 62, instead of dividing by the power ⁇ x 2 (j).
  • the resulted product ⁇ e(j) is outputted as ⁇ h(j).
  • the circuit shown in FIG. 3 can be implemented with the arrangement shown in FIG. 1, except that the supply of the received input signal x(j) and delayed received input signal x(j-M) is not necessary.
  • the scaling factor ⁇ is determined in consideration of the dynamic range of the received input signal.
  • FIG. 4 shows an alternative embodiment of the present invention which is practicable if M is smaller than or equal to N. Specifically, this embodiment omits the first M-sample delay circuit 20, FIG. 1, by using the fact that if M is smaller than or equal to N, the M-samples delayed received input signal x(j-M) is obtainable from the N-sample memory. The rest of the construction is identical with the embodiment shown in FIG. 1.
  • N may be determined on the basis of the impulse response to be estimated. N increases with the duration of the impulse response to be estimated, as stated earlier.
  • any value other than 0 may be selected for M, small M's would increase the correlation between two samples to be processed in parallel and thereby decrease the converging speed.
  • the embodiments have concentrated on particular estimation algorithms, i.e., normalized LMS method and LMS method, the present invention is similarly practicable with an affine projection method or similar algorithm so long as it is based on the LMS method.
  • the present invention increases the converging speed by estimating the impulse responses of two M-sample remote samples at the same time.

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  • Engineering & Computer Science (AREA)
  • Signal Processing (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Cable Transmission Systems, Equalization Of Radio And Reduction Of Echo (AREA)
  • Filters That Use Time-Delay Elements (AREA)
US07/757,951 1990-09-12 1991-09-12 Echo canceller using impulse response estimating method Expired - Fee Related US5289539A (en)

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Cited By (29)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5452289A (en) * 1993-01-08 1995-09-19 Multi-Tech Systems, Inc. Computer-based multifunction personal communications system
US5477534A (en) * 1993-07-30 1995-12-19 Kyocera Corporation Acoustic echo canceller
EP0696126A1 (fr) * 1994-08-01 1996-02-07 Motorola Inc. Méthode et dispositif pour l'estimation du temp d'annulation d'écho
JP2503747B2 (ja) 1990-09-12 1996-06-05 日本電気株式会社 Ｆｉｒ形エコ―キャンセラ
US5546395A (en) 1993-01-08 1996-08-13 Multi-Tech Systems, Inc. Dynamic selection of compression rate for a voice compression algorithm in a voice over data modem
DE19525381A1 (de) * 1995-07-12 1997-01-16 Deutsche Telekom Ag Verfahren zur Steuerung der Schrittweite eines Echokompensators mit adaptivem Filter
DE19525382A1 (de) * 1995-07-12 1997-01-16 Deutsche Telekom Ag Verfahren zur Steuerung der Schrittweite eines Echokompensators mit adaptivem Filter
WO1997002664A1 (fr) * 1995-07-06 1997-01-23 Coherent Communications Systems Corp. Compensation spectrale de bruit destinee a l'annulation d'echo
US5617423A (en) 1993-01-08 1997-04-01 Multi-Tech Systems, Inc. Voice over data modem with selectable voice compression
US5619508A (en) 1993-01-08 1997-04-08 Multi-Tech Systems, Inc. Dual port interface for a computer-based multifunction personal communication system
US5661795A (en) * 1994-08-16 1997-08-26 Sony Corporation Adaptive signal processing device, echo suppressing device and hand-portable telephone device
US5682386A (en) 1994-04-19 1997-10-28 Multi-Tech Systems, Inc. Data/voice/fax compression multiplexer
US5754589A (en) 1993-01-08 1998-05-19 Multi-Tech Systems, Inc. Noncompressed voice and data communication over modem for a computer-based multifunction personal communications system
US5757801A (en) 1994-04-19 1998-05-26 Multi-Tech Systems, Inc. Advanced priority statistical multiplexer
US5757906A (en) * 1993-09-10 1998-05-26 Nec Corporation Method of canceling echoes and echo canceler
US5812534A (en) 1993-01-08 1998-09-22 Multi-Tech Systems, Inc. Voice over data conferencing for a computer-based personal communications system
US5815503A (en) 1993-01-08 1998-09-29 Multi-Tech Systems, Inc. Digital simultaneous voice and data mode switching control
US5864560A (en) 1993-01-08 1999-01-26 Multi-Tech Systems, Inc. Method and apparatus for mode switching in a voice over data computer-based personal communications system
US5909426A (en) * 1997-03-31 1999-06-01 Rockwell Science Center, Inc. Orthogonal LMS algorithms for fast line echo canceler training
US6009082A (en) 1993-01-08 1999-12-28 Multi-Tech Systems, Inc. Computer-based multifunction personal communication system with caller ID
US20030223407A1 (en) * 1993-01-08 2003-12-04 Multi-Tech Systems, Inc. Computer implemented voice over data communication apparatus and method
US6671374B1 (en) 2000-08-03 2003-12-30 Globespanvirata, Inc. Adaptive filter for echo cancellation, method for operating an adaptive filter for echo cancellation, an article of manufacture for determining tap weights and a length for an adaptive filter for echo cancellation and a computer implemented control system for determining tap weights and a length for an adaptive filter for echo cancellation
US20040114752A1 (en) * 2002-12-12 2004-06-17 Adc Dsl Systems, Inc. Fault characterization using information indicative of echo
US20040114729A1 (en) * 2002-12-12 2004-06-17 Adc Dsl Systems, Inc. Fault characterization using information indicative of echo
US20040213293A1 (en) * 2003-04-23 2004-10-28 At&T Corp. Bit and power allocation scheme for full-duplex transmission with echo cancellation in multicarrier-based modems
US7151803B1 (en) 2002-04-01 2006-12-19 At&T Corp. Multiuser allocation method for maximizing transmission capacity
US7522877B1 (en) * 2008-08-01 2009-04-21 Emc Satcom Technologies, Inc. Noise reduction system and method thereof
US20110075833A1 (en) * 2007-10-02 2011-03-31 Adrian Fratila Echo Canceller With Correlation Using Pre-Whitened Data Values Received By Downlink Codec
US8238817B1 (en) 2006-04-12 2012-08-07 Emc Satcom Technologies, Llc Noise reduction system and method thereof

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Cited By (65)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2503747B2 (ja) 1990-09-12 1996-06-05 日本電気株式会社 Ｆｉｒ形エコ―キャンセラ
US6009082A (en) 1993-01-08 1999-12-28 Multi-Tech Systems, Inc. Computer-based multifunction personal communication system with caller ID
US7082106B2 (en) 1993-01-08 2006-07-25 Multi-Tech Systems, Inc. Computer-based multi-media communications system and method
US7542555B2 (en) 1993-01-08 2009-06-02 Multi-Tech Systems, Inc. Computer-based multifunctional personal communication system with caller ID
US5500859A (en) * 1993-01-08 1996-03-19 Multi-Tech Systems, Inc. Voice and data transmission system
US5471470A (en) * 1993-01-08 1995-11-28 Multi-Tech Systems, Inc. Computer-based multifunction personal communications system
US5546395A (en) 1993-01-08 1996-08-13 Multi-Tech Systems, Inc. Dynamic selection of compression rate for a voice compression algorithm in a voice over data modem
US5559793A (en) 1993-01-08 1996-09-24 Multi-Tech Systems, Inc. Echo cancellation system and method
US5574725A (en) 1993-01-08 1996-11-12 Multi-Tech Systems, Inc. Communication method between a personal computer and communication module
US5577041A (en) 1993-01-08 1996-11-19 Multi-Tech Systems, Inc. Method of controlling a personal communication system
US5592586A (en) 1993-01-08 1997-01-07 Multi-Tech Systems, Inc. Voice compression system and method
US7092406B2 (en) 1993-01-08 2006-08-15 Multi-Tech Systems, Inc. Computer implemented communication apparatus and method
US7082141B2 (en) 1993-01-08 2006-07-25 Multi-Tech Systems, Inc. Computer implemented voice over data communication apparatus and method
US5864560A (en) 1993-01-08 1999-01-26 Multi-Tech Systems, Inc. Method and apparatus for mode switching in a voice over data computer-based personal communications system
US5600649A (en) 1993-01-08 1997-02-04 Multi-Tech Systems, Inc. Digital simultaneous voice and data modem
US5617423A (en) 1993-01-08 1997-04-01 Multi-Tech Systems, Inc. Voice over data modem with selectable voice compression
US5619508A (en) 1993-01-08 1997-04-08 Multi-Tech Systems, Inc. Dual port interface for a computer-based multifunction personal communication system
US20060153176A1 (en) * 1993-01-08 2006-07-13 Multi-Tech Systems, Inc. Computer-based multifunctional personal communication system with caller ID
US5673257A (en) 1993-01-08 1997-09-30 Multi-Tech Systems, Inc. Computer-based multifunction personal communication system
US5673268A (en) * 1993-01-08 1997-09-30 Multi-Tech Systems, Inc. Modem resistant to cellular dropouts
US5452289A (en) * 1993-01-08 1995-09-19 Multi-Tech Systems, Inc. Computer-based multifunction personal communications system
US20030223407A1 (en) * 1993-01-08 2003-12-04 Multi-Tech Systems, Inc. Computer implemented voice over data communication apparatus and method
US5754589A (en) 1993-01-08 1998-05-19 Multi-Tech Systems, Inc. Noncompressed voice and data communication over modem for a computer-based multifunction personal communications system
US5815503A (en) 1993-01-08 1998-09-29 Multi-Tech Systems, Inc. Digital simultaneous voice and data mode switching control
US5812534A (en) 1993-01-08 1998-09-22 Multi-Tech Systems, Inc. Voice over data conferencing for a computer-based personal communications system
US5764628A (en) 1993-01-08 1998-06-09 Muti-Tech Systemns, Inc. Dual port interface for communication between a voice-over-data system and a conventional voice system
US5764627A (en) 1993-01-08 1998-06-09 Multi-Tech Systems, Inc. Method and apparatus for a hands-free speaker phone
US5790532A (en) 1993-01-08 1998-08-04 Multi-Tech Systems, Inc. Voice over video communication system
US5477534A (en) * 1993-07-30 1995-12-19 Kyocera Corporation Acoustic echo canceller
US5757906A (en) * 1993-09-10 1998-05-26 Nec Corporation Method of canceling echoes and echo canceler
US6570891B1 (en) 1994-04-19 2003-05-27 Multi-Tech Systems, Inc. Advanced priority statistical multiplexer
US5757801A (en) 1994-04-19 1998-05-26 Multi-Tech Systems, Inc. Advanced priority statistical multiplexer
US6151333A (en) 1994-04-19 2000-11-21 Multi-Tech Systems, Inc. Data/voice/fax compression multiplexer
US6515984B1 (en) 1994-04-19 2003-02-04 Multi-Tech Systems, Inc. Data/voice/fax compression multiplexer
US6275502B1 (en) 1994-04-19 2001-08-14 Multi-Tech Systems, Inc. Advanced priority statistical multiplexer
US5682386A (en) 1994-04-19 1997-10-28 Multi-Tech Systems, Inc. Data/voice/fax compression multiplexer
EP0696126A1 (fr) * 1994-08-01 1996-02-07 Motorola Inc. Méthode et dispositif pour l'estimation du temp d'annulation d'écho
US5661795A (en) * 1994-08-16 1997-08-26 Sony Corporation Adaptive signal processing device, echo suppressing device and hand-portable telephone device
WO1997002664A1 (fr) * 1995-07-06 1997-01-23 Coherent Communications Systems Corp. Compensation spectrale de bruit destinee a l'annulation d'echo
AU697941B2 (en) * 1995-07-06 1998-10-22 Tellabs Operations, Inc. Spectral noise compensation for echo cancellation
US5721730A (en) * 1995-07-06 1998-02-24 Coherent Communications Systems Corp. Spectral noise compensation for telecommunication signal processing
DE19525382B4 (de) * 1995-07-12 2005-12-22 Deutsche Telekom Ag Verfahren zur Steuerung der Schrittweite eines Echokompensators mit adaptivem Filter
DE19525381A1 (de) * 1995-07-12 1997-01-16 Deutsche Telekom Ag Verfahren zur Steuerung der Schrittweite eines Echokompensators mit adaptivem Filter
DE19525381B4 (de) * 1995-07-12 2006-01-05 Deutsche Telekom Ag Verfahren zur Steuerung der Schrittweite eines Echokompensators mit adaptivem Filter
DE19525382A1 (de) * 1995-07-12 1997-01-16 Deutsche Telekom Ag Verfahren zur Steuerung der Schrittweite eines Echokompensators mit adaptivem Filter
US5909426A (en) * 1997-03-31 1999-06-01 Rockwell Science Center, Inc. Orthogonal LMS algorithms for fast line echo canceler training
US8009692B2 (en) 1999-03-25 2011-08-30 At&T Intellectual Property Ii L.P. Bit and power allocation scheme for full-duplex transmission with echo cancellation in multicarrier-based modems
US20090190609A1 (en) * 1999-03-25 2009-07-30 Samuel H. Dworetsky Bit and power allocation scheme for full-duplex transmission with echo cancellation in multicarrier-based modems
US6671374B1 (en) 2000-08-03 2003-12-30 Globespanvirata, Inc. Adaptive filter for echo cancellation, method for operating an adaptive filter for echo cancellation, an article of manufacture for determining tap weights and a length for an adaptive filter for echo cancellation and a computer implemented control system for determining tap weights and a length for an adaptive filter for echo cancellation
US7436893B1 (en) 2002-04-01 2008-10-14 At&T Corp. Multiuser allocation method for maximizing transmission capacity
US7623584B1 (en) 2002-04-01 2009-11-24 At&T Intellectual Property I, Lp Multiuser allocation method for maximizing transmission capacity
US7916802B2 (en) 2002-04-01 2011-03-29 At&T Intellectual Property I, Lp Multiuser allocation method for maximizing transmission capacity
US20100067544A1 (en) * 2002-04-01 2010-03-18 At&T Intellectual Property I, L.P. Multiuser Allocation Method for Maximizing Transmission Capacity
US7151803B1 (en) 2002-04-01 2006-12-19 At&T Corp. Multiuser allocation method for maximizing transmission capacity
US7480367B2 (en) * 2002-12-12 2009-01-20 Adc Dsl Systems, Inc. Fault characterization using information indicative of echo
US20040114729A1 (en) * 2002-12-12 2004-06-17 Adc Dsl Systems, Inc. Fault characterization using information indicative of echo
US20040114752A1 (en) * 2002-12-12 2004-06-17 Adc Dsl Systems, Inc. Fault characterization using information indicative of echo
US7254217B2 (en) 2002-12-12 2007-08-07 Adc Dsl Systems, Inc. Fault characterization using information indicative of echo
WO2004055996A3 (fr) * 2002-12-12 2005-01-20 Adc Dsl Sys Inc Caracterisation de defaillances a l'aide d'informations indiquant un echo
US7512149B2 (en) 2003-04-23 2009-03-31 At & T Intellectual Property Ii, L.P. Bit and power allocation scheme for full-duplex transmission with echo cancellation in multicarrier-based modems
US20040213293A1 (en) * 2003-04-23 2004-10-28 At&T Corp. Bit and power allocation scheme for full-duplex transmission with echo cancellation in multicarrier-based modems
US8238817B1 (en) 2006-04-12 2012-08-07 Emc Satcom Technologies, Llc Noise reduction system and method thereof
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JP2503747B2 (ja) 1996-06-05
CA2051147C (fr) 1996-10-01
CA2051147A1 (fr) 1992-03-13
JPH04120812A (ja) 1992-04-21

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